External fixation systems are used to stabilize fractured bones or hold bones after corrective surgery. They are usually made up of structural members held together by clamps, all assembled by the surgeon during surgery. The clamps are placed on bone pins and are attached to bars, creating a frame to hold the bones in particular relationships. Typically, the external fixation frame is assembled in the configuration the surgeon desires, then the fracture is reduced and the clamps are tightened.
Multi-pin clamps, a common type of component of external fixation systems, are configured to hold two or more bone pins. Typically, these multi-pin clamps include posts that are connected to other fixation system components, such as bars, by separate clamping devices. Some known multi-pin clamps and some known separate clamping devices each have two bolts used to connect them to the other fixation system components. When assembling an external fixation system, this can result in six bolts that need to be tightened. Other known multi-pin clamps have built-in bar clamps or bar clamps that are directly attached to them. These typically don't have the flexibility of positions provided by using an independent clamping device, but they are frequently less costly. These typically have four to six bolts that need to be tightened to lock the fixation system in the final position. Either method often requires that a number of connections are tightened to lock the multi-pin clamp to the pins and to the rest of the external fixation system. Individually tightening these multiple connections can be time consuming and can be confusing and distracting in the operating room.
Furthermore, if the system employs protective sleeves during placement, the problem of adjusting a large number of bolts is compounded. Protective sleeves are used to limit damage to soft tissue caused as the pin is advanced to or screwed into the bone. Protective sleeves are also used as guides where the multi-pin clamps have specific locations for the pins to fit relative to other pins. One common method for maintaining the position of one pin relative to another is to have a protective sleeve guide that holds the pins in a particular relationship to each other while they are driven into bone. Another method includes holding the protective sleeves in the clamps themselves in the same slots that will hold the pin. When using the clamp and a protective sleeve, the clamp has to be tightened onto the sleeves to keep it from slipping and to allow the easy transfer of force from the surgeon to the sleeves. However, both of these methods can create inefficiencies. When using a separate guide, the surgeon has to remove the guide, obtain the clamp, manipulate the clamp over the pins in the proper orientation, and then tighten the clamp onto the pins. The advantage of using the definitive clamp along with protective sleeves is that the clamp can be loosened, the sleeves can be removed from the clamp and the clamp tightened on the final pins without having to relocate the clamp over the pins. The disadvantage is that the surgeon has to provisionally tighten the clamp, typically using a separate wrench for this, then loosen the clamp and retighten it after the pins are placed, again requiring individual loosening and tightening of connections.
As described above, the fixation frame is typically assembled first, then the fracture is reduced. During this reduction phase, the bars and pins may slide in the clamps and the clamps may rotate to the final desired position. In order to maintain rigidity when the clamps are in the final position, some clamps use features that interdigitate with other features. While reducing the fracture, the interdigitating components are typically loosely held together, permitting the components to rotate relative to each other, jumping on the interdigitating features. However, to hold the rods and the pins snugly for final adjustment, the clamps are usually tightened to a load that exceeds the spring force separating the interdigitating features. This makes further adjustment of the fixation system difficult when the rods and pins are snugly held.
For example, helical wire springs that fit into conventional external fixation system clamps have spring rates that range from less than 1 pound per inch to higher than 20 pounds per inch. Loads that completely close the springs are in the single or low double digits. Typical loads achieved by finger tightening are more on the order of 100 to 200 pounds. This means the springs compress and interdigitating components completely come together well before the user can generate any significant clamping load on the pins or rods. If the surfaces have features that interdigitate with each other, adjustment of the clamp once some clamping load has been applied can be difficult, with the components catching and jumping when adjusted.
The system of the present disclosure is directed to overcoming one or more of the shortcomings of prior devices.